[5.2.1] | Regression | Revert PR #2281 SNIProxy code change (#2395) (#2436)

Author: DavoudEshtehari

src/Microsoft.Data.SqlClient/netcore/src/Microsoft/Data/SqlClient/SNI/SNIProxy.cs

@@ -653,10 +653,10 @@ private bool InferConnectionDetails()
 
                 Port = port;
             }
-            // Instance Name Handling. 
-            if (backSlashIndex > -1)
+            // Instance Name Handling. Only if we found a '\' and we did not find a port in the Data Source
+            else if (backSlashIndex > -1)
             {
-                // This means that there is a part separated by '\'
+                // This means that there will not be any part separated by comma.
                 InstanceName = tokensByCommaAndSlash[1].Trim();
 
                 if (string.IsNullOrWhiteSpace(InstanceName))

src/Microsoft.Data.SqlClient/tests/ManualTests/SQL/InstanceNameTest/InstanceNameTest.cs

@@ -87,6 +87,7 @@ public static void ConnectManagedWithInstanceNameTest(bool useMultiSubnetFailove
         }
 
 #if NETCOREAPP
+        [ActiveIssue("27824")] // When specifying instance name and port number, this method call always returns false
         [ConditionalFact(nameof(IsSPNPortNumberTestForTCP))]
         public static void PortNumberInSPNTestForTCP()
         {